1. Field of the Invention
The present invention relates to a method of driving a droplet jetting head for jetting droplets of a specific liquid, a droplet jetting apparatus including the droplet jetting head, and a device manufacturing method using the above method or the apparatus.
Priority is claimed on Japanese Patent Application No. 2004-013029, filed Jan. 21, 2004, the content of which is incorporated herein by reference.
2. Description of Related Art
Generally, a droplet jetting head provided in a droplet jetting apparatus includes a pressure generating chamber for containing a specific liquid, a piezo actuator for compressing the pressure generating chamber, and a nozzle opening communicated with the pressure generating chamber. The liquid in the pressure generating chamber is compressed by the piezo actuator, thereby jetting a small amount of liquid from the nozzle opening as a droplet. The liquid close to the nozzle opening directly contacts the outside air; thus, viscosity is increased due to the dry atmosphere. When the viscosity is increased, the nozzle opening is clogged, so that droplet jetting may not be satisfactorily performed.
In order to prevent substandard droplet jetting, flushing is performed regularly or irregularly in which droplets are forcedly jetted from the droplet jetting apparatus so as to discharge the thickened liquid (having high viscosity) outside the pressure generating chamber. When the substandard droplet jetting cannot be solved by flushing, attraction of the thickened liquid via the nozzle opening of the droplet jetting head is performed and then the surface of the nozzle plate is cleaned with a wiper. Examples of the known cleaning method are disclosed in the following documents: Japanese Unexamined Patent Application, First Publication Nos. 2002-079693 and 2003-118133.
As explained above, flushing is performed for preventing clogging of the droplet jetting head and cleaning is further performed when clogging occurs. If clogging still remains, flushing and cleaning are repeatedly performed. Therefore, the amount of liquid discharged from nozzles which are not clogged is increased and thus liquid is uselessly consumed. In addition, if cleaning is repeatedly performed and the plane in which the nozzle opening is formed is repeatedly wiped, the life of the wiper is reduced and water repellency of the plane in which the nozzle opening is formed is also reduced, thereby causing substandard droplet jetting.
Furthermore, recently, the droplet jetting apparatus is used for manufacturing various devices such as color filters or micro lens arrays used in liquid crystal display devices, or other devices having micro patterns. In addition, a plurality of droplet jetting heads are used for improving throughput (i.e., the number of devices which can be manufactured per unit time) to the utmost. Therefore, reduction of the throughput due to the clogging of the nozzle opening must be prevented as much as possible.